Heat-driven showers and thunderstorms could pop up this afternoon across parts of both islands.  Isolated, but slow-moving, these cells could produce significant rainfall.

The biggest thunderstorm threat is from Taranaki to Taupo and in the higher elevations of the Wanganui hill country.  There is a chance that these storms could produce small hail and gusty winds in addition to the heavy rain.  The risk here is moderate.

North of this area, extending to around Hamilton, there is a small risk for thunderstorms.  However, Hamilton has a fair amount of cloud cover this morning.  In areas without a lot of changes in elevation, a fair amount of sunshine is needed to help lift the air and build up the clouds.  So, without some sunshine today, chances for showers and thunderstorms about the northern Waikato will fizzle.

There is also a risk for thunderstorms about the inland areas of the upper South Island as well.  But the risk here is pretty low.

-WeatherWatch.co.nz